At the start of the American Civil War he volunteered for service. President Abraham Lincoln gave him a temporary appointment in the Navy and sent him in the steamer Baltic to the relief of Fort Sumter. Fox could not relieve the fort before Confederate bombardment forced its surrender, but afterwards he brought away the garrison.

Gustavus V. Fox

On August 1, 1861, Lincoln appointed him Assistant Secretary of the Navy, an office which he held until the close of the Civil War. In 1866, he was sent on a special mission to Russia; he conveyed the congratulations of the President to TsarAlexander II upon his escape from assassination. His voyage was made in the monitorMiantonomoh, which was the first vessel of this class to cross the Atlantic. They were accompanied by Augusta.

Fox, Gustavus V. (1882), An Attempt to Solve the Problem of the First Landing Place of Columbus in the New World. Report of the Superintendent of the U. S. Coast and Geodetic Survey (Appendix No. 18, June 1880), Washington: Government Printing Office.